We have developed a new micro air pump, which is driven by a single piezoelectric actuator. In this paper, its pumping mechanism is studied numerically. It is shown that the phase difference between two vibrating disks in the air pump, a diaphragm driven by a piezo actuator and a disk vibrated passively by pump room pressure, plays a critical role to generate net flow rate. The phase difference is set to be a desirable value by adjusting the thickness of the passive vibration disk.
